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Question DetailsAsked on 2/11/2016

Zinc strips for clay tile roofs in the South, ie Florida. Yes or No

My parents live in Fla. I have a lot of experience in the Midwest, but don't know the Florida market very much. There is a continual maintenance issue there, always power-washing the clay tile roofs. Do the zinc strips talked about in other posts work well down there and can they be used with Clay tile applications.?

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ExteriorUpgrader - clay tile and "high profile" stone roofs are a problem in this way - because while actually they are much less damaged by growth on the roof than wood or asphaltic shingles (as long as it is not so thick that it blocks drainage downslope), cleaning them risks the chemicals weakening or creating porous structure in the tiles/stone or partly dissolving it, and of course they are generally a lot more sensitive to being walked on so you can trade a clean roof for cracked, leaking tiles.

My personal recommendation is to avoid walking on tile roofs if at all possible - and certainly on arched or elevated tiles where basically the only safe way to walk on them is on 4" foam pads (mattress and lounger pad foam) or using foam pad "block shoes" that roofers use on that type roof. NOT a thing for amateurs or your run of the mill pressure washing companies to do - should be done by a tile roofing expert if at all, and preferably from a snorkel truck if at all possible.

As mentioned previously, because of their high profile and smooth surface, most clay tiles do not respond well to copper or zinc based algae/moss treatments because the high spots do not get hit or wash off quickly (in case of granular or spray treatments) though granted the lower areas where metallic treatments will settle are usually the worst affected by growth and the first to start backing up, so the granular copper and zinc (I prefer the latter because less staining risk) can halp out, but unlikely to give uniform effect. Spraying with a liquid zinc based compound will certainly kill moss and most algaes and lichen (there are a couple of species that seem to thrive on it), but that leads to the continual maintenance you are talking about because it only lasts at most a year or two - less in heavy rain areas like most of the Gulf and Florida.

Bleaches and oxy cleaners will also kill them, but with almost guaranteed bleaching and streaking of the roof surface, and many (or most) tiles have a certain amount of lime-based composition which is dissolved by the bleaches and oxy cleaners, so each cleaning etches the surface and actually opens up more pores for dirt/dust to accumulate in and for the algae and moss to root in. Of course, glazed tiles are more resistant to this than natural clay tiles, and fully fired ceramic tiles (surface actually melted) more resistant than just kiln-dried tiles - or worst, sun-dried tiles.

There are some adhesive-based long-term spray treatments that claim to bond the zinc or copper particles (note copper WILL stain/discolor most roofs) for long-term protection even on the high points and on barrel tiles - personally the only ones I have used were on copper roofs, and their long-term performance was not impressive - seemed to either not have much effect, or maybe washed off quickly.

Personally, I think the constant washing of roofs in the South may have more to do with the weather being such that people spend a lot of time in their yards and porches so they see and notice the roof a lot more - combined with a tendency to have trees close by the house for shade. Whereas in the midwest and west and northeast the amount of "yard" time is a lot less so the roof growth does not get noticed so much, I think people tend to keep trees away from the house more to avoid possible windstorm damage, plus in most areas away from the Gulf and Florida (and Hawaii) you do not have the almost daily showers that provide the continuing mosture needed for roof growth to thrive. The (my impression) far greater percentage of one-story houses in Florida also contributes greatly to the visibility of the roof and noticing growth on the roof - in traditional 2 story (or higher) housing areas generally only the neighbors notice the roof growth - not the owner. The constant outdoor weather in Florida also appears to lead to a greater concern for the outside appearance of the house - people down there seem to spend a lot more time and $ on exterior appearance, landscaping, and such than in the north of the mason dixon line areas like ours.

One other thing I have read about Gulf and beach area roof issues is some areas have issues with natural "fertilizing" of the roofs by birds perching on them, which could certainly promote such growth.

One last through on the zinc strip - on a clay tile roof retrofitting it could be a hassle, because it is designed to be nailed through shingles - easy to pull asphalt shingles back a bit to nail in under the tab, not so easy with clay tiles - you cannot hid the nail holes and should probably predrill for the fasteners - through I guess you might be able to gob asphaltic sealant or epoxy in under the bottom edgge of shingles and then jam the zinc strip in an inch or so. Don't know how well that would hold in hurricane and tornado and thunderstorm windburst country like Florida. Personally, since the metal ions will just follow the low (drainage) path anyway and not hit a lot of the low spots in the tiles if a textured or wavy pattern, I would go with periodic chemical kill and washing off, brushing and scraping as needed, or with sprayed on zinc solution (which avoid walking on the roof at all).

Whether you worry about it or not - most manufacturers say do nothing about it till it gets thick enough that it might be causing backup of water (blocking downslope drainage) then scrape and brush (pressure washing not recommended) the growth off then let go for another 5 years or so.

Answered 4 years ago by LCD


Will work to limit algae and moss growth (mostly the former in most of FL unless under trees) - however, it can cause gray streaking and staining on lighter colored and red/orange tiles, though what I have seen has looked more like weathering dirt and less obtrusive than algae growth.

Now the cavet - if your tiles are high profile rther thann flat - stick up a lot in part of their profile, or are the extreme in high profile (half barrel tile) the zinc runoff from the strip will only protect the lowest lying areas where the runoff occurs, not the part sticking up mostly above the runoff zone. To get uniform treatment for those areas, you need to have it sprayed with liquid MossOut or similar algecide periodically.

One other thing on the zinc treatments, and many others - many deep south clay tile roofs do not have gutters, so the runoff can leave a whitish or grayish white residue and staining on patios and pavers and such.

Answered 4 years ago by LCD


LCD, thanks for the update. My parents are down in Venice. I recently visited and could not believe the amount of maintenance down there on tile roofs. Plus, the amount of growth on the roofs. So, my natural tendancy is to try to find a solution. But, it is out of my wheelhouse of experience. I was hoping you would respond to the question.

Thanks again, keep up the good work.

Exterior Upgrader is owner of

Euro-Tech, Inc.

Servicing much of Illinois and Wisconsin


Answered 4 years ago by ExteriorUpgrader

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